There has been so far a refrigerant channel switching unit disposed between a heat source unit and a utilization unit of an air conditioning system and configured to switch flow of refrigerant. For example, an air conditioning system disclosed in Japan Laid-open Patent Application Publication No. 2008-39276 includes a plurality of refrigerant channel switching units installed between a heat source unit and a plurality of utilization units. Each of the refrigerant channel switching units is provided with a first refrigerant pipe, a second refrigerant pipe, a third refrigerant pipe and a coupling portion. The first refrigerant pipe is provided with a switch valve and is connected to a suction gas communicating pipe extending from the heat source unit. The second refrigerant pipe is provided with a switch valve and is connected to a high-low pressure gas communicating pipe extending from the heat source unit. The third refrigerant pipe is connected to a gas pipe extending to the utilization unit. The coupling portion couples these refrigerant pipes. In this type of refrigerant channel switching unit, it is required to bypass refrigerant from the second refrigerant pipe to the first refrigerant pipe in order to prevent the refrigerant from stagnating within the second refrigerant pipe when the utilization is in a thermo-off state, a deactivated state or the like.